In U.S. Pat. No. 4,655,156, the disclosure of which is incorporated herein by reference, there is described a flotation system based on modular floats. Such floats are generally hollow and are formed of polymeric material, usually polyethylene, typically by blow molding, although other techniques, such as roto-molding may be used.
Certain jurisdictions do not permit hollow floats to be employed in docks and the like, in view of a perceived danger of flooding upon puncture or fracture, and such hollow floats usually are foam filled for such jurisdictions. Foam filling can be effected by forming polyurethane foam in situ. Polyurethane foam formation is relatively easy to perform in the enclosed environment of the interior of the float but suffers from the drawback that the reactants are relatively expensive when compared with other foaming systems.
Polystyrene is commercially available in the form of pre-expanded beads which are heat-expandable and fusible to a foam structure. Such materials have been employed to foam fill hollow floats, using steam jets to provide the heat required for expansion. Polystyrene beads are much cheaper than polyurethane foam reactants. However, such polystyrene bead expansion process suffers from the drawbacks that several openings are required for the steam jets and must be closed water tight by welding or the like before the float can be used and free water formed upon steam condensation remains in the float or must be permitted to evaporate from the interior of the float, necessitating a long dry-out storage period. In addition, the foam structure which is achieved is rather poor, with pockets of loose non-expanded beads in areas where the steam could not reach.